In the field of graphic arts, an image forming system having super high contrast (in particular, a gamma (G) of at least 10) is required for improving the reproduction of continuous tone by dot images or the reproduction of line images.
For this purpose, a specific developer called "lith developer" has hitherto been used. The lith developer consists of hydroquinone as the developing agent and also contains a sulfite as a preservative in the form of an addition product with formaldehyde, whereby the concentration of free sulfite ions is reduced as low as possible (typically below 0.1 mol/liter). Accordingly, the lith developer is susceptible to air-oxidation and thus cannot be stored for over 3 days.
Methods of obtaining high contrast and high sensitivity photographic characteristics using a stable developer and hydrazine derivatives are described in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,211,857, 4,243,739, etc. Furthermore since sulfite can be added at a high concentration, the stability of the developer to air oxidation is greatly improved as compared to the lith developer.
However, for forming super high contrast images using a hydrazine derivative, the pH of the developer must be at least 11.0. In such circumstances, the developing agent is liable to be oxidized, the pH is liable to deviate by absorbing CO.sub.2 from the air and stable photographic properties are thus not obtained. Accordingly, a process of obtaining super high contrast images in a developer having a high sulfite ion concentration at a pH below 11.0 has been desired.
A means for increasing the activity of hydrazine has been keenly desired and in this regard, phosphonium salt compounds in JP-A-61-167939 (the term "JP-A" as used herein mean as "unexamined published Japanese patent application"), disulfide compounds in JP-A-61-198147, and amine series compounds in JP-A-60-140340 are disclosed as contrast enhancing agents. However, even by using these compounds, it is difficult to further enhance contrast at a pH below 11.
On the other hand, a low-speed, light-sensitive material for safelight use employing a hydrazine compound, and containing a water-soluble rhodium salt, is disclosed in JP-A-60-83038 and 60-162246. However, in this case, the addition of a sufficient amount of rhodium salt to increase the sensitivity obstructs the increase of contrast by the hydrazine compound, whereby the desired sufficiently high contrast images are not obtained.